Broach



J. A. PSENKA Aug. 10, 1965 BROAGH 2 Sheets-Sheet 2 Original Filed April10, 1961 INVENTOR. JOSEPH A.PSENKA 7 1 g Jag/" 41 I 7 fATTORNEYS UnitedStates Fatent O 3,19,i72 BRUAQH Joseph A. Psenira, Eloorniieid Hills,Mich, assigner to National Breach Machine Qonrpany, Wayne, Mich, acorporation of Michigan Original application Apr. til, 1961, Sci. N101,887. Divided and this appiication Oct. 21, B64, Scr. No. 405,412

Qiairns. (GE. 29-951) The present invention relates to a breach and is adivision of my present application, U.S. Serial No. 101,887, filed April10, 1961. More particularly this invention relates to a broachcomprising a plurality of sections, a leading one which is a roughingsection adapted to rough out the teeth of a gear or splined element, anda following one in the form of a finishing section adapted to finish theteeth of the workpiece with extreme accuracy.

Breaches of the type described have been utilized in the industry.However, certain problems have been encountered. One of the mainproblems is that the side of the part which is produced by the obtuseside of the broach has more stock removed from it than from the side ofthe part which is produced by the acute side of the breach. This usuallyresults in the acute side not cleaning up fully so that the errors ofform introduced into the part by the roughing section of the broach arenot entirely corrected or eliminated by the side shaving shell formingthe finishing section of the broach.

The present invention relates primarily to means for correcting errorsof form in the breach part which are introduced into the part by theroughing section of the broach. This is accomplished by providing animproved side shaving shell which is adapted to be mounted at the rearof the roughing section of the breach so as to conpletely remove theaforesaid errors.

It is an object of the present invention to provide a breach of thecharacter described in which the finishing section is connected to theleading roughing section in such a manner that the finishing sectionwill locate itself accurately in the workpiece and will thereforeproduce teeth on the workpiece which, for practical purposes, have thesame accuracy as the teeth on the finishing section of the breach.

Another object of the present invention is to provide a breach whichincludes a side shaving shell having the teeth thereon so arranged as toequalize the amount of stock removed from both the acute and the obtusesides.

A further object of the present invention is to provide a breach whereinthe teeth thereon are arranged so that the backotf angle on the acuteside is greater than the backoif angle on the obtuse side so as toincrease the resistance of the tool to move into the obtuse side of thepart.

A still further object of the present invention is to provide a breachhaving a series of longitudinally aligned finish cutting teeth forfinishing a groove in a workpiece, each of the teeth being provided witha front cutting face having an acute side and an obtuse side, each ofthe sides being inclined or tapered inwardly away from the side walls ofthe groove from the front face to the rear of the tooth, with the angleof inclination or taper on the acute side being greater than the angleof inclination or taper on the obtuse side.

Another object of the present invention is to provide a breach assemblycomprising a leading section having stepped longitudinally alignedseries of rough cutting teeth, a following section connected to theleading section, said following section having a series oflongitudinally aligned finish cutting teeth for finishing a groove in aworkpiece, each of said finish cutting teeth having a steam FatentedAug. 1%, 1965 front cutting face having an acute side and an obtuseside, each of said sides being inclined or tapered inwardly from theside walls of the groove from the front face to the rear of the tooth,with the angle of inclination or taper on the acute side being greaterthan the angle of inclination or taper on the obtuse side, and meansmounting the following section on the leading section to maintain theteeth in substantial alignment.

it is thus another object of this invention to provide a simplified lowcost structure of the aforementioned type having certain advantagescontributing to efficiency, reliability and long life as Well as case ofmaintenance.

Gther objects and features of the invention will become apparent as thedescription proceeds, especially when taken in conjunction with theaccompanying drawings illustrating preferred embodiments of theinvention, wherein:

FIGURE 1 is a side elevation of the breach assembly.

FIGURE 2 is a side elevation of the leading roughing section of thebreach.

FIGURE 3 is an end view of the leading section of the breach seen fromthe right in FIGURE 2.

FIGURE 4 is an enlarged view of adjacent teeth illustrated in FIGURE 1taken on the line 4-4 thereof.

FIGURE 5 is an enlarged view of adjacent teeth illustrated in FIGURE 1taken on the line 5-5 thereof.

FIGURE 6 is an elevational view of the novel side shaving shell.

FIGURE 7 is an end view of the shell shown in FIGURE 6.

FIGURE 8 is a view of the teeth looking in the direction of line 8-8 ofFIGURE 6.

FIGURE 9 is a diagrammatic view of a side shaving finishing tooth.

In the broaching of internally toothed members, such as internal gears,spline members or the like, it is possible to produce broaching elementshaving substantially any required degree of accuracy. However, in use,such a breaching element can reproduce itself with substantially perfectaccuracy only when it is not subjected to negative factors occasioned byan earlier stage of the breaching operation. The present inventionrelates to a broach which has a roughing section and a finishingsection, with the finishing section taking the form of a replaceableside shaving shell which is afiixed to and lo cated on the rear end ofthe breach body following the roughing section, such as disclosed in myPatent 2,987,801 which issued on June 13, 1961. Certain aspects of theinvention may be embodied in a finishing broach construction whetherformed as a part of a breach including the finishing construction orformed as a separate broach.

Referring now to the drawings, the leading section of the breachassembly it) is shown in FIGURES 1 and 2 and is designated by thenumeral ill and comprises a head 1?; adapted to be connected to asuitable device for pulling the broach through a hole in a workpiece.Conveniently, the roughing section of the broach is indicated generallyat 14 and includes a series of continuous interrupted annular blades orribs 16 adapted to form separate cutting teeth 29. The rear part of theroughing section includes alternate round and spline teeth. The roundteeth or blades 18 are adapted to machine the hole in the workpiece totrue cylindrical formation. The spline cutting teeth 26 areprogressively stopped from front to rear and are backed off on the topat an angle phi and the sides thereof are relieved to within x inch to 6inch of the top of the profile. The round teeth 13 are also backed offat an angle alpha.

it will be appreciated that the cutting teeth 26 are arranged in axialalignment if the breach it? is for the purpose of producing spur teeth,or in helical alignment if the broach is for the purpose of producinghelical teeth. The

U term longitudinal alignment or the like is intended'to coverarrangemerns for producing both spur and helical ears.

At the following end of the roughing section 14 of the broach assembly10 is a cylindrical support 22 having a reduced portion 24 which forms ashoulder 26. Roan wardly of the reduced portion 24 a support portion 22is threaded as indicated at 23. Rearwardly of the threaded portion 28 isprovided a cylindrical support portion 3%.

Directly to the rearof the final blade of the roughing section 14 thereis a cylindrical surface 32, the opposite sides of which are machinedaway as indicated toforrn rearwardly facing fiat abutment surfaces 34and radially outwardly facing flat surfaces 36. This arrangementprovides a fiat transversely extending key 38'. As shown in FIGURE1,.the following finishing broach section or side shaving shell db isassembled on the support portion 22 of the leading section 11.Rearwardly of the finishing section'or shell id is located a spacer 41followed by a round shell 42 comprising a plurality of continuous rounduninterrupted blades or ribs 44. The finishing shell 4%, spacer landside shaving shell 42 are retained on the support portion 22 of theleading section 11 in assembled relation by nut 48 threaded to thethreaded portion '23 of the leading broach section 11. v

1 The finishing section or shell 49 is essentially tubular in shapehaving toothed cutting blades 59 forming longitudinally aligned seriesof cutting teeth 52. Again, the cutting teeth extend in axially disposedseries if the broach id is tO fOIITl a spur member and the series arehelically aligned if the broach 10 is used to produce helical'teeth onthe workpiece. At the leading end of the finishing section at a notch orkeyway is provided which extends diametrically across the leading endthereof and is dimensioned to receive the key 33 at the following end ofthe roughing section of the broach. The finishing section it? isgenerally provided with a central opening,'the intermediate portion ofwhich is enlarged to provide clearance and the ends of which are ofslightly reduced size to provide guide surfaces which are guidinglyreceived on the cylindrical surface of the support portion 22 of theleading section 11 of the broach lit It will be observed inFlGURE 1 thatthe nut 48 has the front portion or forward end thereof engageable withthe rear end of the round shell ;2 so as to urge the spacer 41 intoengagement with the shoulder 26. With such a key and keyway constructionbetween the roughing and finishing sections a small clearance in theamount of .002 inch is sufiicient to permit limited circumferentialrelative movement between the roughing and finishing broach sections. Inaddition, the key and keyway constructions of the sections are properlyrelated with respect to the cutting teeth thereon so that the cuttingteeth 52; on the finishing section are in substantial true alignmentwith the teeth 29 of the roughing section. Nevertheless,

as the finishing section db moves into action, it is per- The widths ofthe side shaving teeth increase from front a to rear. The broachassembly just described is disclosed in the aforesaid Patent 2,987,801.

Certain problems have been encountered with the use of side shavingshells 40 of the type just described in that the side of the part whichis produced by the obtuse side of the broach has more stock removed fromit than from V the side of the part which is produced by the acute sidenot eliminated by the side shaving shell in a practical length of shell.

FIGURE 6 shows a finishing shell designated by the numeral 54 which isconstructed and designed to correct the aforesaid condition. Shell 54has a series of longitudinally aligned. side cutting teeth 56 whichprogressively increase in width. 'In order to prevent the obtuse side ofthe broach shell Sdfrom removing more material from the part on circulartooth thicknesses than the acute side, it has been found that changingthe backoff angle on the acute side will be of some benefit incorrecting the errors of form. FlGURE 9 shows a tooth 56a having acutting edge 58, with the acute side backed off at an angle phi and theobtuse side backed off at an angle alpha, with the angle phi beinggreater than the angle alpha. Withsucn a construction, the greater thebackoff angle on the acute side, the freer will be the cutting actionthereon and the less tendency there will be to pull the part into theobtuse side and conversely, the lower the backoff angle on theobtuseside, the greater will be the tendency for resistance of the broach tomove into the obtuse side of the part. i f

Originally, finishing shells of the type described had a three-quarterdegree backoff angle on both the acute and obtuse sides of the teeth forboth spur and helical. However, due to size reduction of the tool withsuccessive face grindings that produce'd'undersized parts in arelatively short time, the backoff angles were decreased to one-halfdegree on both sides of the'teeth on both spurand helical applications.found that the aforesaid problem is substantially eliminated bydecreasing the obtuse backoff angle to onequarter degree and increasingthe acute backoif angle to three-quarter degree. The net result is abroach that has as much tool life as if both sides were backed off toonehalf of a degree. V

The drawings and the foregoing specification constitute a description ofthe improved broach in such full, clear, concise and exact terms as toenable any person skilled in the art to practice the invention, thescope of which is indicated by the appended claims.

What I claim as my invention is:

l. A broach having a series of longitudinally aligned finish cuttingteeth for finishing a groove in a workpiece, each of said teeth having afront cutting face having an acute side and an ob-tuseside, each of saidsides being inclined inwardly away from the side walls of the groovefrom the front face to the rear of the tooth, withthe angle ofinclination on the acute side being greater than the angle ofinclination on the obtuse side.

2. A broach assembly comprising a leading section having steppedlongitudinally aligned series of rough cutting teeth, a followingsection connected to the leadingsection,

said following section having a series of longitudinally aligned finishcutting teeth for finishing a groove in a workpiece, each ofsaid finishcutting teeth having a front cutting face having an acute side and anobtuse side, each of said sides being inclined inwardly from the sidewalls of the groove from the front face to the rear of the tooth, withthe angle of inclination on the acute side being greater than the angleof inclination on the obtuse side, and means mounting said followingsection on said leading section to maintainsaid cutting teeth insubstantial alignment.

3. A broach having a series of longitudinally aligned finish cuttingteeth for finishing a groove in a workpiece,

. each of said teeth having a front cutting face having an of thebroach. This results sometimes in the acute side not cleaning upentirely so thatthe errors of form introduced into the broach part bythe roughing section are acute side and an obtuse side, each of saidsides being tapered inwardly away from the side Walls of the groove fromthe front face to the rear of the tooth, with the angle of taper on theacute side being'greater than the angle of taper on the obtuse side.

t. A broach assembly comprising a leading section having'steppedlongitud-inally aligned series of rough cuttingf With the presentinvention, it has been teeth, a following section connected to theleading section, said following section having a series oflongitudinally aligned finish cutting teeth for finishing a groove in aworkpiece, each of said finish cutting teeth having a front cutting facehaving an acute side and an obtuse side, each of said sides beingtapered inwardly from the side walls of the groove from the front faceto the rear of the tooth, with the angle of taper on the acute sidebeing 6 greater than the angle of taper on the obtuse side, and meansmounting said following section on said leading section to maintain saidcutting teeth in substantial alignmerit.

Noreferences cited.

ANDREW R. JUHASZ, Primary Examiner.

1. A BROACH HAVING A SERIES OF LONGITUDINALLY ALIGNED FINISH CUTTINGTEETH FOR FINISHING A GROOVE IN A WORKPIECE, EACH OF SAID TEETH HAVING AFRONT CUTTING FACE HAVING AN ACUTE SIDE AND AN OBTUSE SIDE, EACH OF SAIDSIDES BEING INCLINED INWARDLY AWAY FROM THE SIDE WALLS OF THE GROOVEFROM THE FRONT FACE TO THE REAR OF THE TOOTH, WITH THE ANGLE OFINCLINATION ON THE ACUTE SIDE BEING GREATER THAN THE ANGLE OFINCLINATION ON THE OBTUSE SIDE.